Self-powered systems such as, for example, arrays of wireless standalone sensors require an in-situ electricity generator. These systems are often complex and comprise numerous elements which are sometimes installed out of reach. In these situations, maintenance of the system is complicated and costly if, for example, a discharged battery replacement were to become necessary. It is therefore desirable not to replace the battery throughout the lifetime of the system in order to reduce the maintenance costs and eliminate the associated waste products.
It is in this context that electricity generators equipped with energy harvesters have been proposed. Energy harvesting is based on the use of energy sources freely available in the environment such as light, temperature changes, vibrations or similar, to generate electricity. For this conversion, an energy converter is used.
At the output of the energy converter, it is desirable to harvest the energy at a high useful voltage to be easily formatted by a load powered by this electric generator without too much energy wastage.
Thus, it has been proposed, in the application WO 2007/063194, to use a collection circuit and a control device for this collection circuit which make it possible to transfer the energy generated by the converter to the load to be powered only when this energy has reached a sufficient threshold.
Thus, the known electricity harvesters comprise:                a source of energy to be harvested,        an energy harvester, this harvester comprising:                    a first converter equipped with first and second connection terminals, this first converter being suitable for converting a variation of the energy to be harvested into a corresponding excess of electrical charges on the first connection terminal relative to the second terminal,            a collection circuit for collecting the excess of electrical charges on the first connection terminal, this circuit being equipped:                            with an output terminal via which the collected charges are delivered, and                a first controllable switch connected to the first connection terminal, this first switch being suitable for switching between an open position in which it prevents the discharging of the electrical charges through the first connection terminal and a closed position in which it allows the discharging of the electrical charges through the first connection terminal, and                                    a control device for the first switch designed to control the switching of this switch to its closed position when the excess of electrical charges present on the first connection terminal exceeds a first predetermined threshold.                        
As described in the application WO 2007/063194, the solid state switches of the collection circuit are typically transistors or thyristors. It is known practice to power these switches from electrical charges produced by the first converter so as to allow a standalone operation of the energy harvester, that is to say by using only the energy to be harvested.
Prior art is also known from U.S. Pat. No. 6,522,048 B1, EP 1 426 995 A1 and from the paper by Dimitry Zakharov et al.: “Thermal energy conversion by coupled shape memory and piezoelectric effects”, Journal of Micromechanics & Microengineering, volume 22, No. 9, 24 Aug. 2012, page 99005.